This invention relates to a method of manufacturing a semiconductor device and, in particular, to a manufacturing method for removing undesirable nitride regions by using a sacrificial oxide film.
In the process of manufacturing semiconductor devices such as field effect transistors, the semiconductor devices on the silicon substrate are separated by a field insulation film or an STI (Shallow Trench Isolation) film.
JP H8-107205A discloses a technique for separating the semiconductor devices by the field oxide film which is formed by the LOCOS (Local Oxidation of Silicon) method. During the field oxidation process, nitride films are also oxidized so that nitrogen atoms (N) or ammonium molecules (NH3) are produced and form undesirable nitride regions in field regions. In order to remove the undesirable nitride regions, a sacrificial oxide film is formed on the silicon substrate. Then, the silicon substrate is soaked in hydrofluoric acid solution to remove the undesirable nitride regions together with the sacrificial oxide film.
According to JP H8-107205A, the sacrificial oxide film is formed in the atmosphere comprising ozone. However, the temperature of the atmosphere should be lower than 800° C. because the thermal-resistivity of ozone is very poor.
The semiconductor devices on the silicon substrate may be separated by the STI film. During the process of forming the STI film, undesirable nitride regions are also formed on the silicon substrate. One of existing methods of removing the nitride region is to carry out dry or wet oxidation. However, during the dry or wet oxidation, the oxidizing species may diffuse into the STI film and oxidize the silicon substrate in the trench.
The oxidized STI film will expand and apply stresses to the device formation regions adjacent thereto. Such stresses may result in the increase of the junction leakage current.